Hi McD,
I wouldn't do it. It's very limiting because the performance of a subwoofer is partly dependent on its location within your specific room and its interaction with the room's dimensions. Putting it in a big cabinet prevents you from finding the best location for the sub in your room. Can you not hide it in one of the corners?
Speaking generally, subwoofers and speakers already have their own carefully designed enclosures and are meant to sound their best in relatively free space, with no additional obstructions or cabinetry interfering with the designer's intentions.
The sound will be compromised. Why buy really neutral transparent-sounding speakers to downgrade all that performance by sticking them into large cabinetry? Bookshelf speakers may be quite pleasing on open shelving. However, as soon as you put them into enclosed cabinetry, you in effect horn-load them, which really degrades the tonal neutrality.
Regards,
Alan
